In recent years, there has been a concern for depletion of fossil fuel such as petroleum or coal, and expectation for sustainably-usable renewable energy has been rising. As the renewable energy, a solar cell, wind power generation, and the like can be cited. Because these depend on weather and a natural situation in a power generation amount, there is a problem that stable supply of electric power is difficult. Therefore, there has been made an attempt to store the electric power generated by the renewable energy in a storage battery and stabilize the electric power. However, when the electric power is stored, there are problems that a cost is required for the storage battery and a loss occurs at a time of storage.
For such points, attention is being given to a technology of performing water electrolysis using the electric power generated by the renewable energy to produce hydrogen (H2) from water or reducing carbon dioxide (CO2) electrochemically to convert it into a chemical substance (chemical energy) such as a carbon compound such as carbon monoxide (CO), a formic acid (HCOOH), methanol (CH3OH), methane (CH4), an acetic acid (CH3COOH), ethanol (C2H5OH), ethane (C2H6), or ethylene (C2H4). When these chemical substances are stored in a cylinder or a tank, as compared with when the electric power (electric energy) is stored in the storage battery, there are advantages that a storage cost of energy can be reduced and a storage loss is also small.
As an electrolytic device for carbon dioxide, for example, the structure in which a cathode solution and CO2 gas are brought in contact with a cathode, and an anode solution is brought in contact with an anode is being studied. As a specific configuration of the electrolytic device, for example, there is known a structure in which an ion exchange membrane as a separator is sandwiched by a cathode solution flow path and an anode solution flow path, and the cathode and the anode are each disposed on a surface on a side opposite to a surface in contact with the separator of each of the solution flow paths. When a reaction to produce CO from CO2 is performed by passing a constant current through the cathode and the anode using the electrolytic device having such a structure, there is a possibility that a trouble such as a large variation in a cell voltage occurs. At this time, there is a tendency for a voltage variation of the anode to be larger than a voltage variation of the cathode.